Proximal tubule microvilli remodeling and albuminuria in the Ren2 transgenic rat.

TG(mRen2)27 (Ren2) transgenic rats overexpress the mouse renin gene, with subsequent elevated tissue ANG II, hypertension, and nephropathy. The proximal tubule cell (PTC) is responsible for the reabsorption of 5-8 g of glomerular filtered albumin each day. Excess filtered albumin may contribute to PTC damage and tubulointerstitial disease. This investigation examined the role of ANG II-induced oxidative stress in PTC structural remodeling: whether such changes could be modified with in vivo treatment with ANG type 1 receptor (AT(1)R) blockade (valsartan) or SOD/catalase mimetic (tempol). Male Ren2 (6-7 wk old) and age-matched Sprague-Dawley rats were treated with valsartan (30 mg/kg), tempol (1 mmol/l), or placebo for 3 wk. Systolic blood pressure, albuminuria, N-acetyl-beta-D-glucosaminidase, and kidney tissue malondialdehyde (MDA) were measured, and x60,000 transmission electron microscopy images were used to assess PTC microvilli structure. There were significant differences in systolic blood pressure, albuminuria, lipid peroxidation (MDA and nitrotyrosine staining), and PTC structure in Ren2 vs. Sprague-Dawley rats (each P < 0.05). Increased mean diameter of PTC microvilli in the placebo-treated Ren2 rats (P < 0.05) correlated strongly with albuminuria (r(2) = 0.83) and moderately with MDA (r(2) = 0.49), and there was an increase in the ratio of abnormal forms of microvilli in placebo-treated Ren2 rats compared with Sprague-Dawley control rats (P < 0.05). AT(1)R blockade, but not tempol treatment, abrogated albuminuria and N-acetyl-beta-d-glucosaminidase; both therapies corrected abnormalities in oxidative stress and PTC microvilli remodeling. These data indicate that PTC structural damage in the Ren2 rat is related to the oxidative stress response to ANG II and/or albuminuria.

Oxidative stress and glomerular filtration barrier injury: role of the renin-angiotensin system in the Ren2 transgenic rat.

TG(mRen2)27 (Ren2) transgenic rats overexpress the mouse renin gene, manifest hypertension, and exhibit increased tissue ANG II levels and oxidative stress. Evidence indicates that elevated tissue ANG II contributes to oxidative stress, increases in glomerular macromolecular permeability, and consequent albuminuria. Furthermore, angiotensin type 1 receptor (AT1R) blockers reduce albuminuria and slow progression of renal disease. However, it is not known whether improvements in glomerular filtration barrier integrity and albuminuria during treatment are related to reductions in oxidative stress and/or kidney renin-angiotensin system (RAS) activity. To investigate the renal protective effects of AT1R blockade, we treated young (6-7 wk old) male Ren2 rats with valsartan (Ren2-V; 30 mg/kg) for 3 wk and measured urine albumin, kidney malondialdehyde (MDA), RAS component mRNAs, and NADPH oxidase subunits (gp91(phox) and Rac1) compared with age-matched untreated Ren2 and Sprague-Dawley (S-D) rats. Basement membrane thickness, slit pore diameter and number, and foot process base width were measured by transmission electron microscopy (TEM). Results indicate that AT1R blockade lowered systolic blood pressure (30%), albuminuria (91%), and kidney MDA (80%) in Ren2-V compared with untreated Ren2 rats. Increased slit pore number and diameter and reductions in basement membrane thickness and podocyte foot process base width were strongly associated with albuminuria and significantly improved following AT1R blockade. AT1R blockade was also associated with increased angiotensin-converting enzyme-2 and neprilysin expression, demonstrating a beneficial shift in balance of renal RAS. Thus reductions in blood pressure, albuminuria, and tissue oxidative stress with AT1R blockade were associated with improved indexes of glomerular filtration barrier integrity and renal RAS in Ren2 rats.

Nonalcoholic steatohepatitis and the cardiometabolic syndrome.

Nonalcoholic fatty liver disease (NAFLD) is now considered to be the most common liver disease in the United States and involves a spectrum of progressive histopathologic changes. Common risk factors associated with NAFLD include obesity, diabetes, and hyperlipidemia. Although most patients with NAFLD have simple hepatic steatosis, a significant number develop nonalcoholic steatohepatitis, which may progress to fibrosis, cirrhosis, or end-stage liver disease. There is increasing evidence that NAFLD is a common feature in patients with the cardiometabolic syndrome, a onstellation of metabolic, cardiovascular, renal, and inflammatory abnormalities in which insulin resistance is thought to play a key role in end-organ pathogenesis. NAFLD is usually diagnosed after abnormal liver chemistry results are found during routine laboratory testing. No therapy has been proven effective for treating NAFLD/nonalcoholic steatohepatitis. Expert opinion emphasizes the importance of exercise, weight loss in obese and overweight individuals, treatment of hyperlipidemia, and glucose control.

Microalbuminuria and proximal tubule remodeling in the cardiometabolic syndrome.

Microalbuminuria is a simple screening test that is not only associated with an increased risk of progressive renal insufficiency, but also an increased risk of cardiovascular disease and stroke in the cardiometabolic syndrome. The role of oxidative stress, inflammation, and cellular-extracellular matrix remodeling fibrosis is very important, and the authors have previously observed that albuminuria is related, in part, to loss of the integrity of the glomerular filtration apparatus. The proximal tubule may play a more important role than previously thought, as it is estimated that in health this portion of the nephron reabsorbs 5-8 g of albumin that normally leaks through the glomerulus on a daily basis. Recently, the authors have made important preliminary observational findings regarding proximal tubule microvilli remodeling and oxidative stress, which may help to explain microalbuminuria. These observations suggest that albuminuria is associated with proximal tubule injury, as well as loss of integrity of the glomerular filtration barrier in association with obesity and insulin resistance.